JAMB Biology 2006 Past Questions & Answers

Mendel's second law, also known as the Law of Independent Assortment, states that the alleles for one trait separate into gametes independently of the alleles for another trait. This means that the inheritance of one characteristic, like seed colour, does not affect the inheritance of another characteristic, like seed shape. Therefore, the alleles for different traits segregate independently during the formation of sex cells (gametes).

Common mistake: Students often mistakenly choose option C because the independent segregation of chromosomes during meiosis is the physical basis for Mendel's second law, but the law itself is stated in terms of alleles, not the chromosomes they are on.

Variation means there are differences among individuals in a population. When the environment changes, for example, through a new disease or a shift in climate, some individuals may possess traits that help them survive these new conditions. These survivors can then reproduce, passing on their useful traits and ensuring the species continues to exist.

Common mistake: Students may mistakenly choose option B, as favoured traits do become dominant, but this is a result of the main advantage, which is the population's ability to adapt to environmental changes.

In humans and many other animals, sex is determined by a pair of sex chromosomes. A female normally has two X chromosomes, which is written as XX. A male normally has one X chromosome and one Y chromosome, written as XY. Therefore, the two normal types of sex chromosome combinations are XX for females and XY for males.

Common mistake: Students often mistakenly choose options containing XXY or XYY because they confuse the normal sex chromosome combinations with abnormal ones that cause genetic disorders like Klinefelter syndrome (XXY).

Identical twins have the exact same genetic information (genotype) because they develop from a single fertilized egg. However, a person's final appearance and characteristics, known as their phenotype, are influenced by both their genes and their environment. Factors like diet, exercise, and lifestyle can cause differences in growth, which explains why Hassan is taller and fatter despite having the same genes as Hussain.

Common mistake: Students often mistakenly choose options A or C because they forget that identical twins have the same genes, and they incorrectly assume that any physical difference must be due to genetics alone.

Exponential growth is a specific pattern where a population's growth rate becomes more rapid in proportion to its increasing size. A key feature of this pattern is that the population doubles in size at constant, regular intervals, assuming resources are unlimited. This type of growth, when plotted on a graph, produces a characteristic J-shaped curve.

Common mistake: Students often confuse exponential growth with a sigmoid growth curve, which shows growth slowing down and stabilizing as it reaches the environment's carrying capacity.

Typhoid fever is a serious bacterial infection caused by the bacterium Salmonella typhi. This microorganism is usually spread through contaminated food and water, which is common in areas with poor sanitation. The infection leads to symptoms like high fever, headache, and stomach pain.

Common mistake: Students might mistakenly choose Shigella because it is also a bacterium that causes a serious intestinal disease called dysentery, which is also spread through contaminated food and water.

Clayey soil is composed of very fine particles that are tightly packed together. Although it is rich in mineral nutrients, these nutrients are held so tightly to the surfaces of the clay particles that they are not easily released for plant roots to absorb. Therefore, the nutrients are present but not readily available for the plant's use.

Common mistake: Students often mistakenly choose sandy soil because they know it is poor for agriculture, but this is because it has large particles and cannot hold onto nutrients at all, not because the nutrients are present but unavailable.

Grasses in the savanna have special underground structures called perennating organs, such as rhizomes. When a bush fire occurs, it burns the leaves and stems above the ground, but these underground organs are protected from the heat. After the fire passes, these organs use their stored food to quickly sprout new shoots, allowing the grass to recover and grow again.

Common mistake: Students often choose 'rapid growth' because it describes the recovery, but this growth is only possible because the protected perennating organs survived the fire to begin with.

Shelter belts are rows of trees and shrubs planted specifically to protect an area from strong winds. In the Sahel region, the dry and dusty Harmattan wind is a major ecological factor that causes soil erosion. The primary purpose of planting these trees is to act as a physical barrier to slow down or 'break' the force of the wind, thus protecting the soil and farmland.

Common mistake: Students often choose 'check desert encroachment' because while breaking the wind does help prevent desertification, the direct and primary purpose of a shelter belt is to manage the wind itself.

A climax community is the final, mature stage of ecological succession, where the ecosystem has reached a state of balance. In this stage, the types of plants and animals are well-adapted to the environment and to each other, leading to a community that does not change much over time. This stability means the composition of plant and animal species remains relatively constant.

Common mistake: Students often mistakenly choose options suggesting change because the overall process of succession involves change, but they forget that the 'climax' community is the final, stable endpoint of that process.